The present invention relates generally to bearings for gear pumps. More particularly, it relates to an improved bearing with a pulsed bleed hole configuration with intent to minimize cavitation damage.
Gear pumps often comprise two gears, usually of similar configuration, that mesh with each other inside a housing. A first or drive gear is an extension of a drive shaft; as it rotates, it drives a second gear, commonly called the driven gear. As the gears rotate within the housing, fluid is transferred from an inlet to an outlet of the pump. The drive gear must carry the full power load of the pump. The gears are highly stressed at high pressures and high loads. Gears of either spur or helical configuration can be used; although spur gears are most common.
The volume of fluid pumped through a gear pump partially depends on the depth of the tooth, the tooth count, and the width of the gear. Larger volumetric output is realized when lower gear tooth counts with large working tooth depths and face width are used. Most pumps have gears with ten or twelve teeth.
As a spur gear rotates, individual "segments" of fluid are released between the teeth to the outlet, thereby pulsing or rippling the output flow.
A problem that occurs with larger gear pumps operated at high speeds is cavitation erosion of the surfaces of the gear teeth and/or bearings. Cavitation erosion results in pitting of the surfaces of the gear teeth and bearings that eventually can result in degraded pump volumetric capacity and affect pump durability. As the gears rotate and go through their mesh cycle, an opening inter-tooth volume is formed. As the volume increases in size from minimum to maximum, the pressure within this volume decreases and vapor bubbles or cavities are formed. As the gears rotate and the volume is further filled, this volume is subjected to higher pressure. As a result, the vapor formed within the inter-tooth volume is forced back into solution. The energy associated with this change of phase is significant and, in effect, the vapor cavity implodes on the gear teeth and bearing surfaces thus resulting in cavitation damage to these surfaces.
Existing gear pump designs are known in the art, including the following: U.S. Pat. Nos. 4,097,206; 4,193,745; 3,003,426; 2,981,200; and 2,774,309.
Accordingly, it has been considered desirable to develop a new and improved bearing with a pulsed bleed hole configuration which would overcome the foregoing difficulties and others while providing better and more advantageous overall results in a simple manner.